Commitments and Contingencies - Environmental (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) sites	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) sites	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Accrued obligations for environmental matters, current liabilities	$ 65		$ 65
Environmental Issue
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites	223		223
Number of environmental superfund sites (in sites) | sites	17		17
Liability for third-party tort claims	$ 14		$ 14		$ 15
Future costs for environmental liabilities, minimum	290		290
Future costs for environmental liabilities, maximum	525		$ 525
Site Contingency, Estimated Time Frame for Accrued Cost Distributions			10 years
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	395	$ 427	$ 404	$ 435
Accruals	2	3	3	5
Payments	(9)	(14)	(19)	(24)
Ending balance	$ 388	$ 416	$ 388	$ 416